The sealing of passageways, ducts and the like with a removable seal which permits the ducts upon removal of the seal to be moved laterally with respect to each other has proved to be a troublesome task in installations where during operation the passageways have a limited amount of differential movement. For instance, in the sealing of an ash hopper to the lower end of the furnace of a steam generator, it is necessary to provide an arrangement where a seal is maintained notwithstanding three dimensional movement of the furnace with respect to the ash hopper. As the furnace heats up upon initiating operation, the furnace extends downwardly and it expands laterally outward in all directions. In installations employing a continuous operating submerged scraper in the hopper, it is necessary that periodic maintenance be had with respect to the hopper mechanism. In order to provide suitable access for this maintenance, the hopper must be capable of moving laterally outward from beneath the steam generator. Thus, the seal must be removable as well as being capable of accommodating the differential movement caused by the thermal expansion of the furnace.
One conventional method of providing such a sealing arrangement for this type of ash hopper is to provide pivoted plates secured to the lower end of the steam generator. These plates extend in one position downward from the steam generator into the water contained within the ash hopper thus effecting a seal between the steam generator and the hopper. When it is desired to move the hopper laterally from beneath the steam generator, the plates are pivoted through a suitable motor operating mechanism to a horizontal position thus being withdrawn from the ash hopper. The hopper may then be moved to its lateral remote position. This is a relatively expensive and complicated sealing system which is not without its problems with respect to maintenance.